A ‘Swiss Cheese’ Approach Can Give Us A Second Chance To Contain COVID-19

Fifteen years ago, in response to the threat of H5N1 avian influenza, my team at the White House developed the National Strategy for Pandemic Influenza. We recognized that the world would have to make its way through the first wave of a pandemic, and possibly the second wave, without a vaccine.

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Led by Drs. Richard Hatchett and Carter Mecher, we worked with disease modelers and key stakeholders to develop a strategy of early, coordinated interventions such as school closures and social distancing to delay and lower the peak of illnesses and to reduce the total number of cases in communities. Two years later we published this guidance, along with this now almost iconic graphic. Today this strategy is called flattening the curve.

From the CDC’s “Interim Pre-pandemic Planning Guidance: Community Strategy for Pandemic Influenza Mitigation in the United States”CENTERS FOR DISEASE CONTROL AND PREVENTION​

When explaining the strategy, we asked people to visualize each intervention, such as school closure, as a slice of Swiss cheese — an imperfect barrier to virus transmission as represented by the holes in the cheese. When multiple partially effective interventions are combined early in an outbreak, like stacked Swiss cheese slices, the gaps are covered and virus transmission is slowed, or even stopped.

Governments around the world have implemented variations on this strategy against Covid-19. South Korea was successful with a particularly effective slice: robust testing, contact tracing, quarantine, and isolation. Once it was recognized that Covid-19 was being transmitted in the U.S., states took multilayered approaches to avoid a catastrophic burden on hospitals and save lives. We are just beginning to see the impact of these efforts.

We can’t change the past, but we have a second chance to show we can contain this virus. Widespread stay-at-home restrictions can eventually suppress virus transmission to a level that existed several weeks ago, rewinding the epidemiologic clock and making containment possible once again.

At that point, we can take three steps that will allow us to relax the most restrictive social-distancing measures and reopen our cities:

Require everyone to wear a mask. A cloth mask does not provide substantial protection to the person wearing it, but it can prevent an infected person from transmitting Covid-19 to others. In the lingo of epidemiology, this is called source control. The Centers for Disease Control and Prevention has already recommended that the public use face coverings and published DIY mask instructions, but this is not enough. We need a directive — not just a recommendation – that everyone should wear a cloth mask in public places. This could substantially reduce transmission in communities while making it possible for people to leave their homes. It would also address the thorny problem of transmission of the virus by people who don’t have symptoms.

Several apparel manufacturers have begun producing cloth masks, making it feasible for everyone to have one. Universal source control could be a highly effective layer of Swiss cheese that would allow us to relax other more restrictive measures.

Bring testing to the people. As we relax social distancing, the way to prevent outbreaks is to quickly find people with the virus and stop onward spread through testing, contact tracing, isolation, and quarantine. This requires the availability of testing everywhere, with results available in hours, not days.

To make this work, testing must be available when and where people need it. Drive-through and pop-up testing centers will play a role, but we should also bring testing to people, just as we do with rideshare services and food delivery. Hiring and training a workforce would augment under-resourced public health departments and put people back to work. Workers with medical training could collect samples, supported by an army of non-medical personnel with appropriate personal protective equipment to safely carry out contact tracing and provide guidance on voluntary isolation and quarantine. The technology platforms that power the gig economy could be repurposed and scaled to make this possible across the nation.

The most important enabler of just-in-time testing will be the general public, whose buy-in and sense of personal responsibility can ensure that testing happens when it is needed. It would be ideal for people to seek a test the moment they develop symptoms, as reflexively as grabbing a thermometer if they have a fever.

And if they have Covid-19, isolating themselves and asking their contacts to voluntarily quarantine can help them be the end of the chain of transmission rather than another link in it.

Prepare for Covid-19 rebounds. As we are seeing in Asia, relaxation of social interventions can lead to a resurgence of virus transmission. This will be a risk until we have substantial immunity in the population from a vaccine and/or previous exposure. We need to define triggers to reinstate social interventions early and in a coordinated manner, such as laboratory-based surveillance in the community or our inability to link new cases to known cases. Those triggers and actions should be understood and exercised by all communities.

After this wave of the Covid-19 pandemic, we will have a “new normal” way of living and working that will provide a layer of protection compared to our pre-pandemic life. Early on, we can expect fewer public gatherings, less travel, more social distancing in the workplace, and more virtual interactions. These will certainly reduce the risk of rebound. And if we’ve successfully deployed the first two solutions — masks and testing — we can avoid the most extreme measures that we are experiencing now.

These interventions are the layers of Swiss cheese that can let us reopen our cities while preventing a resurgence of infections. They’ll enable us to flatten a second wave of the pandemic if it comes in the fall — or sooner — but most importantly they will buy us much-needed time until we have a vaccine.

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